BMW OEM Grade Michelin Pilot Sport are apparently a slightly better product than the commerciially available product if you believe Tyre Reviews: https://www.youtube.com/watch?v=COA630Juf_U
How they compare to other brands, I'm not sure. I dont think BMW approve any other brands though. In the UK at least, the price difference for similar "premium brand" products is pretty negligable, especially if you had the "run flats", so I would probably go with the Michelins. But If you aren't fussed about premium brands, and not worried about trade-in value, you can save a pretty penny by shopping around.